1. The Field of the Invention
The present invention relates to a tire intended to be mounted on a rim having at least one first frustoconical seat, the generatrix of which has an axially outer end which is closer to the axis of rotation than the other, axially inner, end. It also relates to a mounted assembly comprising such a tire mounted on a rim.
2. The Related Art
Such a tire is described in the commonly owned U.S. Pat. No. 5,785,781. It comprises at least one first bead, which is intended to be mounted on a first rim seat which is inclined towards the outside. The first bead is of conventional axial width, ends axially to the outside in a bead toe and has a bead seat, the generatrix of which has its axially outer end closer to the axis of rotation than its axially inner end. The generatrix is extended axially to the outside by an outer face defining the bead toe, such face forming with the axis of rotation an angle xcex3, open radially and axially towards the outside, of less than 90xc2x0. The radial carcass reinforcement of the tire is anchored within each bead to at least one inextensible annular reinforcement element and has a meridian profile, when the tire is mounted on its operating rim and inflated to its operating pressure, with a direction of curvature which is constant at least in the sidewall extending the bead which ends in the toe and which is such that, in the bead, the tangent to the point of tangency of the profile with the inextensible annular element of the bead forms with the axis of rotation an angle xcfx86, which is open towards the outside, of at least 70xc2x0.
The bead of such a tire, and more particularly the structure of the hooking of the carcass reinforcement, may be variable. In the aforementioned United States patent, the carcass reinforcement is anchored to an inextensible annular reinforcement element (generally a coated bead wire) in conventional manner, that is to say, by winding the reinforcement around the element to form an upturn starting from the base of the element and rising radially towards the outside.
In this type of tire, the bead structures may be established in order to permit modification (increase) of the clamping of the bead toe on the mounting rim according to the tension of the carcass reinforcement, which results in having initial clamping on the rim of low value, knowing that the clamping will increase when the tire is inflated to its recommended pressure. These bead structures, when the conditions of travel of the tire are such that the beads are brought to high temperature, and at the end of their life, have deficiencies in terms of endurance which result from a certain unwinding of the carcass reinforcement from around the annular reinforcement element of the bead heel, linked with a reduction in the clamping, in particular when the upturn of the carcass reinforcement is short.
In order to overcome these drawbacks, there has been proposed in commonly-owned international patent application No. PCT/EP 99/10471 a novel tire comprising at least one first bead, the seat of which has a generatrix, the axially inner end of which lies on a circle of diameter greater than the diameter of the circle on which the axially outer end is located, the bead heel being axially to the inside. The toe of the bead is axially to the outside. A radial carcass reinforcement winding within each bead extends around at least one inextensible annular heel reinforcement element which is coated with rubber mix, passing from the inside to the outside to form an upturn, extending into a profiled element of rubber mix in the form of a wedge defined by two sides coming from an apex A which is located beneath the section of the annular element. The rubber mix forming the profiled element, axially adjacent to the annular element, has a Shore A hardness greater than the Shore A hardness(es) of the rubber mixes respectively radially above the element and the axially adjacent profiled element. Furthermore, when this tire is mounted on its operating rim and inflated to the recommended pressure, the meridian profile of the carcass reinforcement has a constant direction of curvature in the first bead and the sidewall extending it radially and has a tangent TTxe2x80x2 to the point of tangency T, of the profile with the annular element of the first bead which forms with the axis of rotation an angle xcfx86, which is open towards the outside, and is between 45xc2x0 and 70xc2x0.
In this latter tire bead structure, the inclination of thee carcass reinforcement at the connection with the inextensible annular reinforcement element results in an increase in the axial component of the force exerted by the reinforcement on the annular reinforcement element and makes it possible effectively to increase the clamping of the carcass reinforcement under the annular reinforcement element. However, the fact of using an angle of opening of the carcass reinforcement of between 45xc2x0 and 70xc2x0 to the point of tangency with the annular element may result, in use, in problems of attack at the level of the outer surface of the tire in the region of the sidewalls thereof. In particular, and compared with the tire structure described in U.S. Pat. No. 5,785,781, for which the angle formed by the carcass reinforcement at the point of tangency with the inextensible annular element of the beads is greater than 70xc2x0, the structure described in the aforementioned international application No. PCT/EP 99/10471 results in having sidewalls which are more exposed to various scratching and friction phenomena which adversely affect the aesthetic appearance thereof and may also adversely affect the integrity of the tire. To these attacks of the scratching type there have to be added the impacts to which the sidewalls in accordance with this last described structure are subjected and which may adversely affect the integrity of said sidewalls, including that of the carcass reinforcement.
The tire, according to the invention and viewed in meridian section, comprises at least a first bead, the seat of which has a generatrix, whose axially inner end lies on a circle of diameter greater than the diameter of the circle on which the axially outer end is located, the bead heel being axially to the inside, whereas the bead toe is axially to the outside, and a radial carcass reinforcement winding within each bead around at least one inextensible, annular heel reinforcement element. The carcass reinforcement winding is coated with rubber mix, and passes from the inside to the outside to form an upturn, extending into a profiled element of rubber mix in the form of a wedge having a Shore A hardness greater than the Shore A hardness(es) of the rubber mixes respectively radially above said element and the axially adjacent profiled element. The meridian profile of the carcass reinforcement, when the tire is mounted on its operating rim and inflated to the recommended pressure, has a direction of curvature which is constant in the first bead and the sidewall extending it radially, and has a tangent TTxe2x80x2 to the point of tangency T of the profile with the annular heel-reinforcement element of the first bead which forms with the axis of rotation an angle xcfx86 which is open towards the outside of between 45xc2x0 and 70xc2x0, such tire being characterized in that, viewed in meridian section:
at least the sidewall extending the first bead comprises a profiled element having, viewed in section, substantially the form of a crescent defined by an inner face and an outer face, the profiled element extending between a point P1 and a point P2, the point P1 being located at a distance R1 greater than the external radius Rte of the annular bead element and less than the radius R0 of the circle on which are located the points of the carcass reinforcement axially most to the outside of the tire mounted on its rim and inflated to its use pressure, the point P2 being located at a distance R2 greater than the radius R0, the distances R1 and R2 being measured perpendicular to the axis of rotation of the tire;
one of the inner or outer faces of the profiled element follows the profile of the carcass reinforcement; and
the trace of the face of the profiled element opposite the face of the profiled element closest to the carcass reinforcement has a single direction of curvature.
The profiled element may equally well be placed axially towards the outside or towards the inside of the carcass reinforcement in the sidewalls. Preferably, the angle formed by the tangent to the point PI on that face of the profiled element which is opposite the face closest to the carcass reinforcement with the tangent TTxe2x80x2 is, in absolute value, greater than or equal to 20xc2x0, so as to impart appropriate rigidity to the sidewall and to have a sufficient thickness to protect the sidewall from attack.
Apart from the beneficial role with respect to attack on the sidewalls which is played by the presence of a profiled element in the sidewalls, a beneficial influence is noted on the resistance of the tire according to the invention when the latter is subjected to travel at very low or even zero inflation pressure. In fact, the addition of at least one profiled element of suitable thickness, coupled with the carcass reinforcement (that is to say linked to this reinforcement by a rubber mix), stiffens the sidewall in the radial direction and substantially reduces the loading deformations at fixed load when the pressure is zero. This makes it possible to increase running capacity under these particular/exceptional conditions, in particular even before a bearing support comes into operation to bear the load.
Complementarily, a tire has been produced in accordance with the description of the commonly-owned U.S. Pat. No. 5,785,781; that is, to say a tire comprising at least one first bead, the seat of which has a generatrix, the axially inner end of which lies on a circle of diameter greater than the diameter of the circle on which the axially outer end is located, and a carcass reinforcement, the meridian profile of the carcass reinforcement, when the tire is mounted on its operating rim and inflated to its operating pressure, having a direction of curvature which is constant at least in the sidewall extending said first bead and which is such that, in said bead, the tangent to the point of tangency of said profile with the inextensible annular element of the bead forms with the axis of rotation an angle xcfx86 which is open towards the outside of at least 70xc2x0, to which there has been added:
in at least the sidewall extending the first bead, a profiled element having, viewed in section, substantially the form of a crescent defined by an inner face and an outer face, the profiled element extending between a point P1 and a point P2, the point P1 being located, relative to the axis of rotation, at a distance R1 greater than the external radius Rte of the annular bead element and less than the radius R0 of the circle on which are located the axially outermost points of the carcass reinforcement of the tire mounted on its rim and inflated to its use pressure, the point P2 being located at a distance R2 greater than the radius R0, the distances R1 and R2 being measured perpendicular to the axis of rotation of the tire, one of thexe2x80x94inner or outerxe2x80x94faces of the profiled element following the profile of the carcass reinforcement and the trace of the face of the profiled element opposite the face of said profiled element closest to the carcass reinforcement having a single direction of curvature.
There was also noticed a particularly noticeable beneficial effect on protection from attack of the sidewalls of the tire when the tire is partly or completely deflated. In fact, in that part of the tire which is adversely affected by loading on the roadway, the sidewalls are subjected to flexing towards the outside which exposes the sidewalls to attack. Since this type of tire is intended for travelling in low-pressure (or even zero-pressure) conditions, there results increased susceptibility to external attack. In order to reduce this susceptibility, it is advantageous to provide for the presence of a profiled element as described previously for angles xcfx86 which are open towards the outside of at least 45xc2x0.
The profiled element may be made from rubber mix or plastics material which is compatible with the rubber mixes of the tire.
In a preferred variant, the profiled element is covered with a complementary reinforcement armature over at least a partxe2x80x94between P1 and P2xe2x80x94of its face which is axially opposite the face of the profiled element which is closest to the carcass reinforcement, the complementary armature being formed, for example, of one or more plies reinforced by a plurality of cords or cables which are oriented in the same manner in each ply.
So as to ensure satisfactory anchoring of the profiled element, it is advantageous for the complementary reinforcement armature to be extended radially towards the inside beyond the point P1 of the profiled element along the carcass reinforcement in order, for example, to pass radially beneath the annular element.
In practice, and viewed in meridian section, if the point P1 of the radially innermost profiled element is located close to the point of the annular bead element of maximum circumferential development (in practice the radius R1 of the circle on which the point P1 is located is between Rt and (3Rt+Ro)/4), the excess thickness created by this profiled element may sometimes be the cause of additional heating in that part of the tire which is in the vicinity of the annular element: in fact, the additional flexural strength of that part of the sidewall which is connected to the bead results in an increase in the stresses on the bead. In this latter configuration, and in order to avoid an increase in the stresses in the beads, a decoupling groove is produced which is oriented in the circumferential direction, this groove being open axially and radially towards the outside of the first bead. This groove is defined by a radially inner surface and a radially outer surface such that, viewed in section, the point of intersection K of the two surfaces is located at a distance Rri from the axis of rotation of the tire which is substantially equal to R1 so as to permit operation as an articulation substantially about the point P1. The point of intersection K of the radially inner and outer surfaces defining the groove corresponds to the common point of tangency of the surfaces with a straight line perpendicular to the axis of rotation.
xe2x80x9cDistance substantially equal to R1xe2x80x9d is to be understood to mean a distance which may be less than or greater than R1, the difference between the two distances being less than 20% of R1.
In order to have improved operation when travelling at zero or virtually zero pressure, it is advantageous that, viewed in meridian section, the radially inner surface defining the groove has a point axially and radially to the outside located at a distance from the axis of rotation Rre which is greater than or equal to the distance Rri, and in that the profiles of the surfaces are appropriate to come to bear on one another when travelling at zero or virtually zero pressure and thus to participate in bearing the load.
This groove also has the same advantage in the case of a tire such as described in U.S. Pat. No. 5,785,781, the subject matter of which is hereby incorporated herein by reference.
The tire according to the invention also has the advantage of being able to effect, for one and the same dimension of tire fitted on a given vehicle, substantial lightening of the mounted assembly comprising a mounting wheel, the tire and means making it possible to avoid bulging of the crown of the tire when, on a vehicle, the pressure in the mounted assembly is zero or virtually zero.
The bulging of the crown occurs in that part of the tire which comes into contact with the roadway once the crown having a dual curvature (circumferential and transverse) is no longer applied against the roadway by the internal inflation pressure; there then takes place a sudden variation in curvature, the tire only touching the roadway over the periphery of the imprint.
In the aforementioned international application No. PCT/EP 99/10471, the mounted assembly illustrated comprises a tire mounted on a rim having seats of different diameters and an internal support ring bearing on a cylindrical bearing surface. It is noted that the greatest width of the mounted assembly is given by the axially outermost points of the bead and of the rim. It will be noted that the support ring, in order to be effective, must be sufficiently wide both to block the heel of one of the beads and to support the median part of the tire while reducing the risks of bulging of the crown when travelling at zero pressure. It is advantageous to be able to produce a lighter mounted assembly compared with this last-mounted assembly, retaining the functional characteristics of this assembly, by reducing the width of the rim measured between the axially outermost points.
To this end, there is proposed a rolling assembly formed of a tire according to the invention, a mounting rim and means limiting the bulging of the tire when travelling at zero pressure.
This rolling assembly comprises:
a tire comprising a crown, sidewalls and beads, each bead having a seat having a generatrix, the axially inner end of which lies on a circle of diameter greater than the diameter of the circle on which the axially outer end is located, the bead heel being axially to the inside, whereas the bead toe is axially to the outside, and a radial carcass reinforcement winding within each bead around at least one inextensible, annular heel reinforcement element which is coated with rubber mix, passing from the inside to the outside to form an upturn, extending into a profiled element of rubber mix in the form of a wedge having a Shore A hardness greater than the Shore A hardness(es) of the rubber mixes respectively radially above the element and the axially adjacent profiled element, the meridian profile of the carcass reinforcement, when the tire is mounted on its operating rim and inflated to the recommended pressure, has a constant direction of curvature in each bead and in the sidewalls extending them radially and has a tangent TTxe2x80x2 to the point of tangency T of the profile with the annular element of each bead which forms with the axis of rotation an angle xcfx86 which is open towards the outside and is between 45xc2x0 and 70xc2x0;
a rim comprising two frustoconical seats, the generatrix of each seat forming with the axis of rotation an angle xcex1 of between 4xc2x0 and 30xc2x0, the axially outer end of a generatrix being distant from the axis of rotation by a quantity less than the distance from the axially inner end, the frustoconical seats being defined axially to the outside by protrusions having frustoconical axially inner walls, the rim furthermore comprising support means intended at least to prevent the bulging of the crown of the tire, that is to say, means for forcing the crown to remain in contact with the ground under conditions of travel at zero pressure,
the assembly being characterized in that, when the tire is mounted on its rim and inflated to its operating pressure and is viewed in meridian section:
at least one sidewall extending a first bead comprises a profiled element having, viewed in section, substantially the form of a crescent defined by an inner face and an outer face, such profiled element extending between a point P1 and a point P2, the point P1 being located at a distance R1 greater than the external radius Rte of the armular bead element and less than the radius R0 of the circle on which are located the axially outermost points of the carcass reinforcement when the tire is inflated, the point P2 being located at a distance R2 greater than the radius R0, the distances R1 and R2 being measured perpendicular to the axis of rotation of the tire;
one of the inner or outer faces of the profiled element follows the profile of the carcass reinforcement; and
the trace of the face of the profiled element opposite the face of the profiled element closest to the carcass reinforcement has a single direction of curvature.
The tire according to the invention, which has improved performance with respect to the attack of the sidewalls, makes it possible, while retaining the performance imparted by its bead structure when travelling at low or zero pressure, to effect a reduction in the maximum width of the mounting rim, which results in substantially proportional lightening. Furthermore, the reduction in the rim width involves a reduction in the width of the bearing support, the latter actually being better positioned beneath the tread of the tire (which results in turn in a saving in weight).
The presence of a profiled element in the sidewalls of the tire makes it possible, by an adaptation within the grasp of the person skilled in the art, to reduce still further the width of the support ring: in fact, the extra rigidity of the sidewalls which is imparted by the presence of the profiled elements makes it possible to reduce the width of the support since the sidewalls cooperate with the support to bear the load at zero inflation pressure and to limit the deformations under these conditions. Finally, it is possible to reduce the dimensions of the bearing support to just what is necessary to prevent the tread from xe2x80x9cbulgingxe2x80x9d in contact with the roadway, the sidewalls on their own bearing the load at zero inflation pressure.
On the other hand, the possibility of substantially reducing the width of the mounting rim such that the beads of the tire are located axially to the inside of the axially outermost points of the sidewalls offers the advantage of easy mounting of the tire on the rim which, in particular, no longer necessarily requires the presence of a mounting groove on the rim. This type of mounting is described, for example, in U.S. Pat. No. 5,836,366. There results simplification of the manufacture of the rim and a consequent reduction in the manufacturing costs. In order to go further towards an additional reduction in the weight of the rolling assembly, it is advantageous to provide for the seats of the rim to have identical rim diameters.